There is a type of sale in which a wireless device having a restricted function is sold and the function of the wireless device is unlocked according to a contract with a licensee. Specifically, key information representing that a predetermined function is restricted is stored in a wireless device performing a function according to key information specifying an operation as an initial state, and the function of the wireless device is unlocked by rewriting the key information according to a contract.
A method of updating key information in a wireless device is disclosed in Patent Document 1. According to the method described in Patent Document 1, when a licensee designates a wireless device and requests a support center or the like to unlock a function thereof, the support center generates an upgrade key that is data used to update key information of the designated wireless device and transmits the upgrade key to a terminal of the licensee. The licensee applies the upgrade key received by the terminal to the designated wireless device to update key information. Further, the upgrade key is data that is encrypted by an encryption key specific to the designated wireless device, and is itself specific to the designated wireless device, and thus it is difficult to apply the upgrade key to any other wireless device. This prevents a function from being unlocked in a wireless device that is not under contract using a copy of the upgrade key.